This invention relates generally to sealing methods and assemblies, and more specifically to a assembly and method for sealing the interface between a high pressure steam chest and a steam turbine casing.
A steam turbine includes, generally, a steam chest where high pressure steam is collected and a turbine casing wherein the energy contained within the steam is utilized to rotate a power shaft. Typically, the steam chest is placed on the top surface of the turbine casing, forming an interface between the steam chest and the casing. The top surface of the casing defines a plurality of apertures through which steam flows from the chest into the casing. A valve and a valve seat are positioned in each aperture and the valves are regulated to control the amount of steam passing from the steam chest into the turbine casing, thereby controlling the capacity of the steam turbine.
As a general rule, the efficiency of the turbine increases as the pressure of the steam increases. However, when high pressure steam, for example steam in the area of 1500 pounds per square inch, is used with a steam turbine, interfaces such as the one between the steam chest and the turbine casing subject to such pressures become extremely difficult to seal. The success of such a seal depends on many factors such as mating surface finishes, adequate bolting, temperature gradient, proper seal design, and assembly procedures. Many man hours are usually lost before a sufficiently tight seal is achieved at the interface.